server.js

const express = require('express')
const wsServer = require('ws').Server

const PORT = 5566

// 建立 express 物件並綁定在 port 5566
const server = express().listen(PORT, () => {
  console.log(`Listening on ${PORT}`)
})

const wss = new wsServer({ server })

// 監聽是否有新的 client 連上線
wss.on('connection', ws => {
  console.log('One client has connected.')

  // 監聽 client 傳來的訊息後，再將訊息傳回去
  ws.on('message', data => {
    ws.send(data)
  })

  // 監聽 client 是否已經斷開連線
  ws.on('close', () => {
    console.log('One client has disconnected.')
  })
})